1. Field of the Invention
The present invention generally relates to an apparatus for precisely measuring and supplying liquid used in the field of manufacturing chemicals and medicines. More particularly, it relates to an apparatus for precisely measuring and supplying liquid suitably used in investigations, experiments, or the like, for feeding a small or an intermediate quantity of liquid in increments of a very small quantity.
2. Background Art
An apparatus for precisely measuring and feeding a small or an itermediate quantity of liquid by increments of a predetermined very small quantity for a relatively long time is conventional and widely used. One such apparatus is an apparatus in which a small quantity of liquid is supplied into a head tank through a metering pump and sent by liquid pressure due to a substantially fixed height of the liquid in the tank. Another apparatus fills a tank up with liquid and a predetermined gas pressure is applied to the liquid so as to feed the liquid. In a further apparatus, an injector of the syringe type constituted by a precisely produced set of a cylinder and a piston is filled up with liquid and the liquid is pushed out of the injector by power of a motor driven at a predetermined rotational speed. (For example, disclosure is made in Japanese Utility Model Unexamined Publication No. 121266/76).
In the apparatus using a head tank, however, there has been such a disadvantage that a quantity of liquid to be supplied fluctuates up and down because it is difficult to keep the level of the liquid constant. In the apparatus in which liquid in a head tank is pressurized by a gas, on the other hand, there has been such a disadvantage that as the liquid filling the tank decreases as it is sent out, the whole head pressure decreases to thereby decrease the quantity of liquid to be fed. As a result, it is difficult to limit the fluctuation in flow rate of the liquid so as not to be larger than 2% in the time between the initiation and the completion of supplying the liquid. Therefore, there is large scattering in time of ending the addition of liquid. Further, in the above-mentioned apparatus, there has been such a disadvantage that it is difficult to desirably accurately perform the temporary change in quantity of liquid to be supplied. Moreover, in performing automatic flow rate control in the foregoing apparatus, there has been the disadvantage that it is impossible to precisely and accurately perform detection and measurement of a flow rate of liquid and the control of the flow rate is complicated because the flow rate is very small. Although it is suitable for supplying a very small quantity of liquid, the apparatus which supplies liquid by a fixed quantity by using a motor-driven injector of the syringe-type cylinder and a piston has the following disadvantages. Not only is the accuracy in flow rate reduced as the quantity of liquid to be treated is increased to an intermediate quantity but also it is difficult to maintain the smoothness of cylinder surface or piston surface, the equipment increases in weight, the washing required for the equipment becomes extensive, and the cost of the equipment becomes high.
Recently, in various processing steps in the field of manufacturing chemicals and medicines, such as reaction, dissolution, application, and filling, particularly in the processing accompanying reaction, it has been desired to perform the addition of liquid medicine with an accurate flow rate and to make the flow rate arbitrarily changeable since the respective processing steps have been made precise and complicated. It has been further desired to improve the performance of an apparatus for precisely measuring and supplying a very small quantity of liquid.